You can use Twilio in the UK :) you just have to a) sign up properly (with a card) and b) email them to request international calling.

IIRC (I only use them for SMS) International Outbound rates to the UK are the same as US domestic rates :)

edit: yup, http://www.twilio.com/international-calling-rates

> IIRC (I only use them for SMS) International Outbound rates to the UK are the same as US domestic rates :)

It seems only for landlines, however. I'm always amazed by the obscene rates to call a mobile phone outside of the US. (This isn't exclusive to Twilio and I'm not blaming them)